1. Field
At least one feature relates to wireless communication systems, and more specifically, a scheme to reduce signal degradation by compensating for a Doppler frequency offset.
2. Background
Wireless communication systems are used for many applications including communicating between moving platforms to fixed locations. For example, an aircraft may have a wireless (e.g., radio frequency) link to a current base station. As the aircraft moves, it tracks one sector and monitors other sectors for better pilot/beacon signals to determine if another (e.g., closer, better signal strength) base station is available. If a pilot signal from another base station is detected, a communications handoff from the current base station to the candidate base station may be performed.
Because aircraft typically travel at high speeds, there may be a frequency offset differential, due to a Doppler effect, between the current sector and the candidate sector(s). For example, in a worse case scenario, if an aircraft is moving directly away from the current sector and directly toward an opposite candidate sector, and traveling at 340 meters per second (m/s), the frequency offset may be 1927 Hz with a carrier frequency of 850 MHz. This means that there is an underestimation of the true carrier signal power to interference signal power ratio (i.e., C/I power ratio) of the candidate pilot signal, because the estimator is off in frequency. This results in a lower throughput since a handoff may not be performed properly and thus the receiver is not communicating with the best sector or base station.